Oral contraceptive use not linked to major birth defects

London, Jan 7: Oral contraceptive use just before or during pregnancy is not associated with an increased risk of major birth defects, according to a new large-scale study.

Researchers examined records for nearly 900,000 live births in Denmark, and found that even women who used the pill after becoming pregnant were no more likely to have babies with serious defects than mothers who had never used it.

Oral contraceptives are a leading form of contraception worldwide. When used properly, these are over 99 per cent effective, researchers wrote in The BMJ.

Despite decades of research on the safety of oral contraceptive use, little is known about the association between these drugs that contain sex hormones, and major birth defects, especially among these women who become pregnant while taking the drug or after recently stopping use.

A team of US and Danish researchers carried out a large prospective observational study to examine the association between oral contraceptive use around the time of conception, and into pregnancy, with major birth defects.

All live births, birth defects, and maternal medical conditions were analysed from several national Danish medical registries between 1997 and 2011.

The final analyses included 880,694 live-born infants, 2.5 per cent of whom had a major birth defect - like an orofacial cleft or limb defect - within the first year of life.

Infants with birth defects with known causes, such as foetal alcohol syndrome, or chromosomal aberrations, were excluded. In total, 68 per cent of mothers used oral contraceptives, but stopped more than three months before pregnancy, and 21 per cent never used oral contraceptives.

Overall, 8 per cent recently stopped using oral contraceptives within 0-3 months before pregnancy, and 1 per cent used oral contraceptives beyond pregnancy - both these categories were analysed as exposed.

Findings from the study showed no increased risk of any major birth defect associated with oral contraceptive exposure. The prevalence of major birth defects, per 1000 births, was consistent across each group: 25.1 for never users, 25.0 for oral contraceptive use more than three months before pregnancy, 24.9 for oral contraceptive use within 0-3 months before pregnancy, and 24.8 per cent for oral contraceptive use after pregnancy.

The findings should reassure "women who have a breakthrough pregnancy during oral contraceptive use or even [those who] intentionally become pregnant within a few months of stopping oral contraceptive use (because) any exposure is unlikely to cause her foetus to develop a major birth defect," researchers said.